Production of uranium-carbon alloys



United States Patent PRODUCTKON 0F URANIUM=CARBON ALLQYS Jack Williams,Ahingdon, and Charles Brian Davis,

Didcot, England, assignors to United Kingdom Atomic Energy Authority,London, England No Drawing. Fiied Sept. 2, 1960, Ser. No. 53,634 Claimspriority, application Great Britain Sept. 8, 1959 3 Ciairns. (Cl.7S122.7)

The invention relates to the production of uraniumcarbon alloys.

Methods of production of such alloys are described in United StatesPatent No. 2,569,225, British Patents Nos. 825,041 and 821,287.

A preferred method of producing such alloys is to heat a cold-compactedmixture of uranium and carbon powders, with or without an intermetalliccompound of iron and uranium, to a temperature of 800 to 1125 C. tocause a solid-state reaction between the uranium and carbon.

We have now discovered, that the density of such alloys can beincreased, and porosity decreased, by rapid heating of thecold-compacted mixture to a sintering temperature of 1000 to 1125 C., sothat the heat generated by the exothermic reaction between the uraniumand carbon is utilised in the sintering process. We have found that ifthe compact is plunged into a sintering furnace which is already at thesintering temperature, then the rate of heating is sufliciently fast tomake use of this effect. If the compact is placed in a cold furnace, andthe furnace is then heated up in the usual way, taking several hours toreach the sintering temperature, then the heat of reaction isdissipated. We have found that, using the method of this invention, thetemperature of the compact rises above that of the sintering furnace andin fact rises above the melting point of uranium, so that a liquid phasereaction occurs which leads to the very high densities achieved. Theactual temperature reached by the compact depends on the size of thecompact but is within the range 1200-1450 C.

The uranium-carbon alloys which can be produced according to thisinvention may also include plutonium, which may replace part of theuranium in the starting mixture.

According to the invention, a method of producing a dense uranium-carbonalloy, which may also comprise plutonium, comprises cold-compacting amixture of uranium powder and carbon powder and if desired plutoniumpowder, and then heating the said mixture to a sintering temperature byplunging it into a furnace heated to a temperature of 1000" C. to 1125C., whereby the heat of reaction of the mixture causes its temperatureto rise above the melting point of uranium.

We have found that the rate of rise of temperature of the compactedmixture when it is plunged into the furnace is very rapid and depends onthe size of the compact. It is certainly greater than 100 C. per minuteand may be as high as 500 C. per minute for small compacts.

The nature of the invention will be made more apparent by the followingexamples.

EXAMPLES I TO V Uranium powder of particle size to pass a 300 meshBritish Standard test sieve was mixed with ultrafine graphite inproportions of 95.2% uranium powder to 4.8% graphite, by weight. Samplesof this mixture were mixed with amounts of UFe varying from 0 to 15% byweight of the whole. The mixtures of uranium, graphite and UFe were thencold-compacted at 60 tons/sq. in. in tungsten carbide-lined dies to formcompacts of various sizes. Each compact was placed in an alumina boatand passed rapidly into a vacuum furnace heated to 1100" 3,152,528Patented Dec. 22,, 1964 "ice C. Each compact was estimated to reach amaximum temperature of 1200 C. to 1450 C. in less than 5 minutes. it wasthen heated at 1100 C. for 2 hours. The densities and porosities of theproducts are given in the following table, in which products of similarcompositions, but sintered by placing each compact in an alumina boat inthe cold furnace and then heating the furnace to 1100 C. at the rate of300 C. per hour, with a half-hour degassing period at 550 C., areincluded for comparison.

Table I Weight percent of Density (gm./0C.)

whole Example UFeg 0 Fe Slow Rapid Theoretical heating heating EXAMPLESVI TO IX Similar mixtures to those of Examples I and IV werecold-pressed and sintered as before, except that the proportion ofuranium powder was varied from 95.8 to 94.6% and that of graphitecorrespondingly from 4.2 to 5.4%. The results obtained are shown in thefollowing table, in which products of similar compositions, but sinteredby the slow heating method described in relation to, Examples I to V areincluded for comparison.

Table 11 Weight percent Density (gm/cc.) Weight of whole Examplegerfctcfig 0 mixture G UFe Fe Slow Rapid Theoretical heating heatingTables I and II show that the density of the products is increased bythe method of the invention, compared with sintering by slow heating.

We claim:

1. A method for producing a uranium-carbon alloy of high density and loWporosity comprising mixing a uranium metal powder and carbon powder withone another, cold compacting the mixture, passing the compacted mixtureto a sintering zone maintained at the time of passing of the mixture ata temperature within the range of about 10001125 C., permitting thetemperature of the compact in the sintering zone to rapidly rise for ashort period of time solely as a result of the exothermic heat generatedby the reaction of the mixture at a rate greater than about C. perminute to a temperature between about 1200-1450 C., and thereafterheating the mixture in said sintering zone at a temperature in the rangeof about 1000-1125 C. for a period of time suflicient t effect acomplete sintering of the mixture.

2. A method in accordance with claim 1, wherein plutonium metal powderis mixed with the uranium and carbon.

=3 of the mixture at a temperaturewithin the rarigepf abput 10001125 C.,permitting the temperature of the compact in the sintering zone torapidly rise for a period of time not in excess of about 5 minutessolely as a result of the exotherriiic he'at efifat'ed by the reactionofthe mixture at a rate greater than about 100 (3. per minute to atemperature between about 1200'1450 C., and thereafter heati 'rig themigrture in said ein'tering zone at a tempraturei'fi'the fa'rigeof about1000 1125 C. for

a period of time sufficient to etfect a complete sintering of themixture.

References Cited in the file of this patent UNITED STATES PATENTS

1. A METHOD FOR PRODUCING A URANIUM-CARBON ALLOY OF HIGH DENSITY AND LOWPOROSITY COMPRISING MIXING A URANIUM METAL POWDER AND CARBON POWDER WITHONE ANOTHER, COLD COMPACTING THE MIXTURE, PASSING THE COMPACTED MIXTURETO A SINTERING ZONE MAINTAINED AT THE TIME OF PASSING OF THE MIXTURE ATA TEMPERATURE WITHIN THE RANGE OF ABOUT 1000-1125*C., PERMITTING THETEMPERATURE OF THE COMPACT IN THE SINTERING ZONE TO RAPIDLY RISE FOR ASHORT PERIOD OF TIME SOLELY AS A RESULT OF THE EXOTHERMIC HEAT GENERATEDBY THE REACTION OF THE MIXTURE AT A RATE GREATER THAN ABOUT 100*C. PERMINUTE TO A TEMPERATURE BETWEEN ABOUT 1200-1450*C., AND THEREAFTERHEATING THE MIXTURE IN SAID SINTERING ZONE AT A TEMPERATURE IN THE RANGEOF ABOUT 1000-1125*C. FOR A PERIOD OF TIME SUFFICIENT TO EFFECT ACOMPLETE SINTERING OF THE MIXTURE.